STTD encoding for PCCPCH

ABSTRACT

A circuit is designed with a measurement circuit ( 746 ) coupled to receive an input signal from at least one of a first antenna and a second antenna of a transmitter. The measurement circuit produces an output signal corresponding to a magnitude of the input signal. A control circuit ( 726 ) is coupled to receive the output signal, a first reference signal (η 1 ) and a second reference signal (η 2 ). The control circuit is arranged to produce a control signal in response to a comparison of the output signal, the first reference signal and the second reference signal.

CLAIM TO PRIORITY OF PROVISIONAL APPLICATION

[0001] This application claims priority under 35 U.S.C. § 119(e)(1) ofprovisional application No. 60/119,732, filed Feb. 12, 1999 andprovisional application No. 60/120,609, filed Feb. 18, 1999.

FIELD OF THE INVENTION

[0002] This invention relates to wideband code division multiple access(WCDMA) for a communication system and more particularly to space-timetransmit diversity (STTD) detection for WCDMA signals.

BACKGROUND OF THE INVENTION

[0003] Present code division multiple access (CDMA) systems arecharacterized by simultaneous transmission of different data signalsover a common channel by assigning each signal a unique code. Thisunique code is matched with a code of a selected receiver to determinethe proper recipient of a data signal. These different data signalsarrive at the receiver via multiple paths due to ground clutter andunpredictable signal reflection. Additive effects of these multiple datasignals at the receiver may result in significant fading or variation inreceived signal strength. In general, this fading due to multiple datapaths may be diminished by spreading the transmitted energy over a widebandwidth. This wide bandwidth results in greatly reduced fadingcompared to narrow band transmission modes such as frequency divisionmultiple access (FDMA) or time division multiple access (TDMA).

[0004] Previous studies have shown that multiple transmit antennas mayimprove reception by increasing transmit diversity for narrow bandcommunication systems. In their paper New Detection Schemes for TransmitDiversity with no Channel Estimation, Tarokh et al. describe such atransmit diversity scheme for a TDMA system. The same concept isdescribed in A Simple Transmitter Diversity Technique for WirelessCommunications by Alamouti. Tarokh et al. and Alamouti, however, fail toteach such a transmit diversity scheme for a WCDMA communication system.

[0005] New standards are continually emerging for transmit diversity ofnext generation wideband code division multiple access (WCDMA)communication systems as described in Provisional U.S. PatentApplication No. 60/116,268, filed Jan. 19, 1999, and incorporated hereinby reference. These WCDMA systems are coherent communications systemswith pilot symbol assisted channel estimation schemes. These pilotsymbols are transmitted as quadrature phase shift keyed (QPSK) knowndata in predetermined time frames to any receivers within range. Theframes may propagate in a discontinuous transmission (DTX) mode. Forvoice traffic, transmission of user data occurs when the user speaks,but no data symbol transmission occurs when the user is silent.Similarly for packet data, the user data may be transmitted only whenpackets are ready to be sent. The frames are subdivided into sixteenequal time slots of 0.625 milliseconds each. Each time slot is furthersubdivided into equal symbol times. At a data rate of 32 KSPS, forexample, each time slot includes twenty symbol times. Each frameincludes pilot symbols as well as other control symbols such as transmitpower control (TPC) symbols and rate information (RI) symbols. Thesecontrol symbols include multiple bits otherwise known as chips todistinguish them from data bits. The chip transmission time (T_(C)),therefore, is equal to the symbol time rate (T) divided by the number ofchips in the symbol (N).

[0006] A mobile unit must initially receive and synchronize with dataframes transmitted by one or more remote base stations. Each basestation continually transmits broadcast channel (BCH) data over theprimary common control physical channel (PCCPCH) to identify itself tomobile units within the cell. Referring to FIG. 1, there is a simplifiedblock diagram of a typical diversity transmitter of the prior art. Thetransmitter simultaneously transmits primary and secondarysynchronization codes on respective primary (P-SCH) 150 and secondary(S-SCH) 160 channels to uniquely identify each base station signalreceived by the mobile unit. Circuits 156 and 166 modulate the gain ofthese synchronization codes in response to respective gain factorsGP-SCH on lead 154 and GP-SCH on lead 164. Circuit 170 adds thesynchronization codes and applies them to time switch (TSW) 174 via lead172. Time switch 174 selectively applies the synchronization codes toswitches SW0 134 and SW1 136 in response to the control signal at lead140 as indicated by inset 190. These P-SCH and S-SCH codes aretransmitted as symbol 300 (FIG. 3) in time slot 1.

[0007] Broadcast channel data (BCH) for the PCCPCH are applied tochannel encoder 108 via lead 106 (FIG. 1). Interleaver circuit 110applies the BCH data to space-time transmit diversity (STTD) encodercircuit 112. The STTD encoder produces encoded output data at lead 114for the transmit antenna (Ant 1) and at lead 116 for the diversityantenna (Ant 2). Multiplex circuit 118 produces this STTD encoded BCHdata on leads 120 and 122 at a time corresponding to data symbols 302 oftime slot 1 (FIG. 3). The BCH data are modulated by spreading andscrambling codes on lead 124 and applied to switches SW0 134 and SW1136. These switches SW0 and SW1 selectively multiplex SCH data with BCHdata and pilot symbols in response to a control signal on lead 138 asshown at inset 190. The BCH data at lead 180 are then applied to thetransmit antenna (Ant 1), and the data at lead 182 is applied to thediversity antenna (Ant 2).

[0008] Pilot symbol data for the PCCPCH are applied to lead 100.Diversity circuit 102 generates an open loop transmit diversity (OTD)symbol pattern at lead 104 for the diversity antenna. This OTD patterntogether with the pilot symbol pattern for the transmit antenna is shownat TABLE I for each of the sixteen time slots in a frame. By way ofcomparison, the STTD pilot symbol pattern for diversity antenna (Ant 2)transmission on the dedicated physical data channel (DPDCH) is alsoshown. The pilot symbols at leads 100 and 102 are applied to multiplexcircuit 118. Multiplex circuit 118 selectively applies the pilot symbolsat leads 100 and 102 to leads 120 and 122, respectively, at a timecorresponding to pilot symbols 304 of time slot 1 (FIG. 3). Thus,multiplex circuit 118 multiplexes STTD encoded data symbols 302 with OTDencoded pilot symbols 304. The pilot symbols at leads 120 and 122 arethen modulated with spreading and scrambling code. These modulated pilotsymbols at leads 130 and 132 are further multiplexed with SCH data byswitches 134 and 136, respectively, in response to the control signal atlead 138 as shown at inset 190. The resulting pilot symbols are appliedto transmit and diversity antennas via leads 180 and 182, respectively.TABLE 1 TRANSMIT ANTENNA STTD ANT 2 OTD ANT 2 SLOT B₁ S₁ B₂ S₂ B₁ −S₂*−B₂ S₁* B₁ S₁ −B₂ −S₂ 1 11 11 11 11 11 01 00 10 11 11 00 00 2 11 11 1101 11 11 00 10 11 11 00 10 3 11 01 11 01 11 11 00 00 11 01 00 10 4 11 1011 01 11 11 00 11 11 10 00 10 5 11 10 11 11 11 01 00 11 11 10 00 00 6 1110 11 11 11 01 00 11 11 10 00 00 7 11 01 11 00 11 10 00 00 11 01 00 11 811 10 11 01 11 11 00 11 11 10 00 10 9 11 11 11 00 11 10 00 10 11 11 0011 10 11 01 11 01 11 11 00 00 11 01 00 10 11 11 11 11 10 11 00 00 10 1111 00 01 12 11 01 11 01 11 11 00 00 11 01 00 10 13 11 00 11 01 11 11 0001 11 00 00 10 14 11 10 11 00 11 10 00 11 11 10 00 11 15 11 01 11 00 1110 00 00 11 01 00 11 16 11 00 11 00 11 10 00 01 11 00 00 11

[0009] Turning now to FIG. 2, there is a block diagram showing signalflow in an OTD encoder 102 of the prior art for pilot symbol encoding ofthe transmitter of FIG. 1. The pilot symbols are predetermined controlsignals that may be used for channel estimation and other functions aswill be described in detail. The OTD encoder 102 receives pilot symbolsB₁, S₁, B₂ and S₂ at symbol times T-4T, respectively, on lead 100. Thesepilot symbols are applied to the transmit antenna (Ant 1)via multiplexcircuit 118 and switch SW0 134 as previously described. The OTD encoder102 simultaneously produces pilot symbols B₁, S₁, -B₂ and -S₂ at symboltimes T-4T, respectively, at lead 104 for the OTD diversity antenna (Ant2). The pilot symbol pattern for the transmit and OTD diversity antennasis shown at TABLE I for the sixteen time slots of a frame. Each symbolincludes two bits representing a real and imaginary component. Anasterisk indicates a complex conjugate operation or sign change of theimaginary part of the symbol. Pilot symbol values for the first timeslot for the transmit antenna at lead 104, therefore, are 11, 11, 11 and11. Corresponding pilot symbols for the second antenna at lead 104 are11, 11, 00 and 00.

[0010] The bit signals r_(j)(i+τ_(j)) of these symbols are transmittedserially along respective paths 208 and 210. Each bit signal of arespective symbol is subsequently received at a remote mobile antenna212 after a transmit time τ corresponding to the j^(th) path. Thesignals propagate to a despreader circuit (FIG. 6) where they are summedover each respective symbol time to produce input signals R_(j) ¹, R_(j)², R_(j) ³ and R_(j) ⁴ corresponding to the four pilot symbol time slotsand the j^(th) of L multiple signal paths.

[0011] The input signals corresponding to the pilot symbols for eachtime slot are given in equations [1-4]. Noise terms are omitted forsimplicity. Received signals R_(j) ¹, R_(j) ², R_(j) ³and R_(j) ⁴ areproduced by respective pilot symbols B₁, S₁, B₂ and S₂ . Average channelestimates {circumflex over (α)}_(j) ¹, and {circumflex over (α)}_(j) ²over the four pilot symbols for each antenna are obtained from a productof each received signal and a complex conjugate of its respective pilotsymbol as in equations [5] and [6].

R _(j) ¹=(α_(j) ¹+α_(j) ²)B ₁   [1]

R _(j) ²=(α_(j) ¹+α_(j) ²)S ₁   [2]

R _(j) ³=(α_(j) ¹−α_(j) ²)B ₂   [3]

R _(j) ⁴=(α_(j) ¹−α_(j) ²)S ₂   [4]

{circumflex over (α)}_(j) ¹=(B ₁ *R _(j) ¹ +S ₁ *R _(j) ² +B ₂ *R _(j) ³+S ₂ *R _(j) ⁴)/4   [5]

{circumflex over (α)}_(j) ²=(B ₁ *R _(j) ¹ +S ₁ *R _(j) ² −B ₂ *R _(j) ³−S ₂ *R _(j) ⁴)/4   [6]

[0012] Referring now to FIG. 4, there is a simplified diagram of amobile communication system of the prior art. The mobile communicationsystem includes an antenna 400 for transmitting and receiving externalsignals. The diplexer 402 controls the transmit and receive function ofthe antenna. Multiple fingers of rake combiner circuit 404 combinereceived signals from multiple paths. Symbols from the rake combinercircuit 404, including pilot symbol signals, are applied to a bit errorrate (BER) circuit 410 and to a Viterbi decoder 406. Decoded symbolsfrom the Viterbi decoder are applied to a frame error rate (FER) circuit408. Averaging circuit 412 produces one of a FER and BER. This selectederror rate is compared to a corresponding target error rate fromreference circuit 414 by comparator circuit 416. The compared result isapplied to bias circuit 420 via circuit 418 for generating asignal-to-interference ratio (SIR) reference signal on lead 424.

[0013] Pilot symbols from the rake combiner 404 are applied to the SIRmeasurement circuit 432. The SIR measurement circuit produces a receivedsignal strength indicator (RSSI) estimate from an average of receivedpilot symbols. The SIR measurement circuit also produces an interferencesignal strength indicator (ISSI) estimate from an average ofinterference signals from base stations and other mobile systems overmany time slots. The SIR measurement circuit produces an SIR estimatefrom a ratio of the RSSI signal to the ISSI signal. This SIR estimate iscompared with a target SIR by circuit 426. This comparison result isapplied to TPC command circuit 430 via circuit 428. The TPC commandcircuit 430 sets a TPC symbol control signal that is transmitted to aremote base station. This TPC symbol instructs the base station toeither increase or decrease transmit power by 1 dB for subsequenttransmission.

[0014] Turning now to FIG. 5, there is a diagram showing a weightedmulti-slot averaging (WMSA) circuit 732 of the prior art for channelestimation. In operation, a signal buffer circuit 706 (FIG. 7) receivesindividual frames of data having a predetermined time period of 10milliseconds. Each frame of the PCCPCH is subdivided into sixteen equaltime slots of 0.625 milliseconds each. Each time slot, for example timeslot 528, includes a respective set of pilot symbols 520 and datasymbols 529. The WMSA circuit (FIG. 5) samples pilot symbols frompreferably 6 time slots for a Doppler frequency of less than 80 Hz andfrom preferably 4 time slots for a Doppler frequency of 80 Hz or more.These sampled pilot symbols are multiplied by respective weightingcoefficients α₁, through α_(N) and combined by circuit 526 to produce achannel estimate. This channel estimate is used to correct the phase ofreceived data symbols in time slot 527 estimate for a respectivetransmit antenna.

[0015] Referring now to FIG. 6, there is a despreader circuit of theprior art. Received signals from mobile antenna 212 propagate to thedespreader circuit where they are summed over each respective symboltime to produce output signals R_(j) ¹ and R_(j) ² corresponding to thej^(th) of L multiple signal paths as previously described. Thedespreader circuit receives the i^(th) of N chip signals per symboltogether with noise along the j^(th) of L multiple signal paths at atime τ_(j) after transmission. Both here and in the following text,noise terms are omitted for simplicity. This received signalr_(j)(i+τ_(j)) at lead 600 is multiplied by a channel orthogonal codesignal C_(m)(i+τ_(j)) at lead 604 that is unique to the receiver. Eachchip signal is summed over a respective symbol time by circuit 608 andproduced as first and second output signals R_(j) ¹ and R_(j) ² on leads612 and 614 as in equations [1-2], respectively. Delay circuit 610provides a one-symbol delay T so that the output signals are producedsimultaneously.

[0016] This arrangement advantageously provides additional gain at themobile communication system by multiple path transmit antenna diversityfrom a remote base station. The mobile unit, however, must be compatiblewith base stations having a single transmit antenna as well as basestations having transmit antenna diversity. A problem arises, therefore,when the mobile communication system is initially powered up or when itpasses from one cell to another cell. The mobile unit must not onlydetermine which of several base signals offers a preferable signalstrength. It must also determine whether the base station offerstransmit antenna diversity. If the mobile unit incorrectly decodes areceived signal and assumes no transmit diversity, it loses the improvedgain of transmit diversity. Alternatively, if the mobile unitincorrectly decodes a received signal and assumes transmit diversity,multiple fingers of the rake combiner circuit 404 contribute noise tothe received signal.

SUMMARY OF THE INVENTION

[0017] The foregoing problems are resolved by a circuit designed with ameasurement circuit coupled to receive an input signal from at least oneof a first antenna and a second antenna of a transmitter. Themeasurement circuit produces an output signal corresponding to amagnitude of the input signal. A control circuit is coupled to receivethe output signal, a first reference signal and a second referencesignal. The control circuit is arranged to produce a control signal inresponse to a comparison of the output signal, the first referencesignal and the second reference signal.

[0018] The present invention detects a diversity transmit antenna. Acontrol signal modifies receiver signal processing to correspond to thepresence or absence of the diversity transmit antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A more complete understanding of the invention may be gained byreading the subsequent detailed description with reference to thedrawings wherein:

[0020]FIG. 1 is a simplified block diagram of a typical transmitter ofthe prior art using OTD encoded pilot symbols and STTD encoded datasymbols for the PCCPCH;

[0021]FIG. 2 is a block diagram showing signal flow of pilot symbolencoding in the OTD encoder of the transmitter of FIG. 1;

[0022]FIG. 3 is a diagram of pilot, data and search channel symbols of aPCCPCH time slot;

[0023]FIG. 4 is a simplified block diagram of a receiver of the priorart;

[0024]FIG. 5 is a block diagram showing weighted multi-slot averaging(WMSA) of the prior art;

[0025]FIG. 6 is a schematic diagram of a despreader circuit of the priorart.

[0026]FIG. 7A is a block diagram of a transmit diversity detectioncircuit of the present invention;

[0027]FIG. 7B is a block diagram of another embodiment of a transmitdiversity detection circuit of the present invention;

[0028]FIG. 7C is a block diagram of the measurement circuit 746 of FIG.7A;

[0029]FIG. 8A is a simulation showing cumulative probability ofdetecting the presence of transmit diversity as a function of time forthe embodiment of FIG. 7A;

[0030]FIG. 8B is a simulation showing cumulative probability of notdetecting transmit diversity when present for the embodiment of FIG. 7A;

[0031]FIG. 9A is a simulation showing cumulative probability ofdetecting the absence of transmit diversity as a function of time forthe embodiment of FIG. 7A;

[0032]FIG. 9B is a simulation showing cumulative probability ofdetecting transmit diversity when absent;

[0033]FIG. 10A is a simulation comparing normal and STTD decoding ofsingle antenna transmission for a Doppler frequency of 5 Hz withweighted multi-slot averaging (WMSA); and

[0034]FIG. 10B is a simulation comparing normal and STTD decoding ofsingle antenna transmission for a Doppler frequency of 200 Hz withweighted multi-slot averaging (WMSA).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Referring now to FIG. 7A, there is a first embodiment of a mobileunit of the present invention configured for blind detection of transmitdiversity. This blind detection scheme includes a new implementation ofan algorithm disclosed by A. Wald, Sequential Analysis (1947). Mobileantenna 212 receives multipath signals transmitted by base stationantennas at leads 180 and 182 (FIG. 1), respectively. Diplexer circuit702 couples these received multipath signals to lead 704 during receivemode operation. Doppler frequency estimator circuit 740 is described indetail in copending U.S. patent application Ser. No. 09/224,632, filedDec. 31,1998, and incorporated herein by reference. Doppler frequencyestimator circuit 740 receives the multipath signals on lead 704 andproduces an output signal on lead 742 corresponding to the estimatedDoppler frequency. Delay profile estimator circuit 720 also receives themultipath signals on lead 704. Delay profile estimator circuit 720includes a despreader circuit as in FIG. 6 and a match filter circuit(not shown). The delay profile estimator circuit 720 determines which ofthe received multipath signals should be combined based on the strengthof the matched filter output.

[0036] Operation of the measurement circuit 746 will now be explained indetail with reference to FIG. 7C. The measurement circuit 746 receivespilot symbol data from received multipath signals on lead 704. Channelestimate circuit 750 generates separate diversity signals X₁ and X₂,corresponding to antennas on leads 180 and 182, respectively. Theseseparate diversity signals include pilot symbols from a series of timeslots. Coherent averaging circuit 756 coherently averages the energy ofall received pilot symbol data from the respective antennas at leads 180and 182 from K time slots in response to the Doppler frequency estimatorcircuit output signal on lead 742 and produces signals {tilde over (X)}₁and {tilde over (X₁)} on respective leads 758 and 760. The variable K ispreferably the same number of time slots used by the WMSA circuit ofFIG. 5. It is preferably equal to six time slots for Doppler frequenciesbelow 80 Hz and preferably equal to four time slots for Dopplerfrequencies of 80 Hz or more. Non-coherent averaging circuit 762 thennon-coherently averages the signals {tilde over (X)}₁ and {tilde over(X)}₁ over the respective multipaths and produces signals |{tilde over(X)}₁| and |{tilde over (X)}₂| at leads 764 and 766, respectively, inresponse to the output signal on lead 744 from the delay profileestimator circuit. Ratio circuit 768 produces an output signal λ at lead722 that is a ratio of the signals |{tilde over (X)}₁| and |{tilde over(X)}₂| from the primary antenna at lead 180 and the diversity antenna atlead 182, respectively.

[0037] Comparator circuit 726 compares the output signal λ at lead 722to the first reference signal η₁ and the second reference signal η₂ atleads 723 and 724, respectively. These reference signals are programmedsuch that reference signal η₁ is greater than reference signal η₂. Whenoutput signal λ is greater than reference signal η₁, the comparatorcircuit produces a control signal on lead 728 indicating no transmitdiversity. This control signal is applied to WMSA channel estimatecircuit 732. The WMSA channel estimate circuit sets the channel estimateα_(j) ² at lead 736 to zero, thereby eliminating any noise contributionto the received signal. Phase correction circuit 710 then applies thechannel estimate α_(j) ¹ at lead 734 to the received signal at lead 708from signal buffer 706. The phase correction circuit applies a correctedreceived signal from the primary antenna at lead 180 to rake combinercircuit 712. This rake combiner circuit then combines correctedmulti-path signals from the primary antenna and applies the resultingcombined signal to Viterbi decoder circuit 714. The Viterbi decoderproduces a received signal at lead 716.

[0038] Alternatively, when output signal λ is less than reference signalη₂, the ratio of signals from the primary and diversity antennas is nearunity. The comparator circuit 726, therefore, produces a control signalon lead 728 indicating transmit diversity. The control signal is alsoapplied to WMSA channel estimate circuit 732. The WMSA channel estimatecircuit responsively produces channel estimate signals α_(j) ¹ and α_(j)² at leads 734 and 736, respectively. Phase correction circuit 710 thenapplies both channel estimates to the received signal at lead 708 fromsignal buffer 706. The phase correction circuit then applies correctedsignals from the primary antenna at lead 180 and the diversity antennaat lead 182 to rake combiner circuit 712. This rake combiner circuitthen combines corrected multi-path signals from both antennas andapplies the resulting combined signal to Viterbi decoder circuit 714.The Viterbi decoder produces a received signal at lead 716.

[0039] When output signal λ is less than reference signal η₁ but greaterη₂, the ratio of signals is indeterminate and comparator circuit 726does not change the control signal on lead 728. Thus, WMSA channelestimate circuit continues to produce channel estimates corresponding tothe previous state. Likewise, phase correction circuit 710, rakecombiner 712 and Viterbi decoder 714 continue in the same mode ofoperation until output signal λ exceeds the bounds of one of thereference signals, thereby indicating an unambiguous presence or absenceof diversity. Furthermore, reference signal η₁ and η₂ preferablyconverge to a single value η over time. This sequential convergenceassures sequential detection of diversity or non-diversity over time.

[0040] The simulation output of FIG. 8A shows cumulative probability ofdetecting the presence of transmit diversity as a function of time forthe embodiment of FIG. 7A. The simulation conditions include 40 trafficchannels, each having a gain equal to the PCCPCH. Reference signals η₁and η₂ converge to η linearly over 48 frames for Doppler rates of 5 Hzand 20 Hz and over 24 frames for a vehicular Doppler rate of 200 Hz. Thesimulation shows 99% cumulative probability of detection of a diversityantenna at 250 milliseconds, 145 milliseconds and 30 milliseconds forDoppler frequencies of 5 Hz, 20 Hz and 200 Hz, respectively. Thesimulation of FIG. 8B shows cumulative probability P_(m) of notdetecting transmit diversity when present for the embodiment of FIG. 7A.The simulated probabilities are 1.7×10⁻³ and 1.2×10⁻⁴ for pedestrianDoppler frequencies of 5 Hz and 20 Hz, respectively. No error occurredat a 200 Hz Doppler frequency.

[0041] The simulation output of FIG. 9A shows cumulative probability ofdetecting the absence of transmit diversity as a function of time forthe embodiment of FIG. 7A. Under the same simulation conditions as FIG.8, the simulation shows 99% cumulative probability of detecting theabsence of a diversity antenna at 170 milliseconds, 140 milliseconds and55 milliseconds for Doppler frequencies of 5 Hz, 20 Hz and 200 Hz,respectively. The simulation of FIG. 9B shows cumulative probabilityP_(f) of detecting transmit diversity when not present for theembodiment of FIG. 7A. The simulated probabilities are 6.5×10⁻³,3.6×10⁻³ and 6.1×10⁻⁴ for Doppler frequencies of 5 Hz, 20 Hz and 200 Hz,respectively. No error occurred at a 200 Hz Doppler frequency.

[0042] The blind detection circuit of FIG. 7A, therefore, reliablydetects the presence of transmit diversity in less than 250milliseconds. Moreover, the probability of missing P_(m) an activediversity antenna is less than 1.7×10⁻³ and the probability of falsedetection P_(f) of an absent transmit diversity antenna is less than6.5×10⁻³. This method of detection is highly advantageous when timepermits. No special consideration is required at the base station toaccommodate mobile detection. The mobile relies on a ratio of signalsfrom the primary and diversity antennas for detection. Thus, decoding oftransmitted signals is unnecessary for this method of blind detection.

[0043] Turning now to FIG. 7B, there is a second embodiment of a mobileunit of the present invention configured for Level 3 (L3) messagedetection of transmit diversity. This L3 message is a QPSK-encodedbinary message that is transmitted on the PCCPCH together with otherinformation such as neighboring base stations, Secondary Common ControlPhysical Channel (SCCPCH) offset and base station received power. Themobile unit applies received signals to the delay profile estimatorcircuit 720 and signal buffer circuit 706 as previously described. Thedelay profile estimator circuit applies a control signal correspondingto the Doppler rate of the received signal to the WMSA channel estimatecircuit 732 via lead 728. This control signal determines the variable Knumber of time slots used by the WMSA channel estimate circuit 732 (FIG.5). The mobile unit initially assumes the received signal is STFDencoded and produces a corresponding diversity control signal on lead738. The diversity control signal enables production of channel estimatesignals α_(j) ¹ and α_(j) ₂ at leads 734 and 736, respectively. Phasecorrection circuit 710 receives these channel estimate signals togetherwith the data signals on lead 708 and produces a phase-corrected signalat rake combiner circuit 710. If the received data signal isSTTD-encoded, the rake combiner circuit 712 combines multi-path datasignals from the respective primary and diversity antennas and appliesthem to Viterbi decoder circuit 714. The Viterbi decoder circuit 714decodes the L3 message and produces diversity control signal on lead738. If the L3 message confirms that the original PCCPCH data wasSTTD-encoded, operation of the receiver continues as previouslydescribed. Thus, the mobile unit with STTD realizes a typical 3 dB gainfor a 5 Hz Doppler frequency corresponding to pedestrianindoor-to-outdoor transmission and a typical 0.6 dB gain for a 200 HzDoppler frequency corresponding to vehicular transmission compared tonon-diversity transmission.

[0044] When the L3 message indicates the original PCCPCH data was notSTTD-encoded, however, the Viterbi decoder circuit 714 changes the logicstate of the control signal on lead 738. This non-diversity controlsignal on lead 738 disables the diversity channel estimate α_(j) ² onlead 736. The non-diversity control signal further disables thephase-corrected output from phase correction circuit 710, therebyeliminating noise at the rake combiner circuit 712 due to an absentdiversity signal.

[0045] The received L3 message is degraded at the mobile receiver whenSTTD encoding is incorrectly assumed prior to initial decoding. Thisdegradation is due to noise at the rake combiner circuit fingerscorresponding to the absent diversity antenna. The degradation due tothis noise is shown at the simulated output of FIG. 10A. The simulationcompares normal and STTD decoding of single antenna transmission for aDoppler frequency of 5 Hz with weighted multi-slot averaging (WMSA). Thereceived channel energy to noise ratio (E₀/N₀) increases by only 0.2-0.4dB for a selected bit error rate (BER). A comparable result is evidentfrom the simulation comparing normal and STTD decoding of single antennatransmission for a Doppler frequency of 200 Hz with WMSA (FIG. 10B). Thereceived channel energy to noise ratio (E₀/N₀) for this vehicularDoppler frequency of 200 Hz increases by 0.6-0.7 dB for a selected biterror rate (BER). A nominal degradation of the received channel energyto noise ratio (E₀/N₀) of 0.2-0.7 dB at the mobile unit will not inhibitcorrect demodulation of the L3 diversity message. This method ofdiversity detection is highly advantageous in reducing diversitydetection time. The L3 message affirmatively indicates the presence orabsence of diversity transmission at the output of the Viterbi decoderin less than 30 milliseconds. Only nominal signal degradation occurs byincorrectly decoding a non-diversity L3 message as though it were STTDencoded.

[0046] Although the invention has been described in detail withreference to its preferred embodiment, it is to be understood that thisdescription is by way of example only and is not to be construed in alimiting sense. For example, advantages of the present invention may beachieved by a digital signal processing circuit utilizing a combinationof hardware and software operations as will be appreciated by those ofordinary skill in the art having access to the instant specification.Furthermore, the advantages the blind detection method of diversitydetection of FIG. 7A and the L3 message diversity detection of FIG. 7Bmay be combined. For example, the mobile unit may initially use theblind detection method to determine a presence or absence of transmitdiversity. The result of this determination may then be used to decodethe L3 message from the base station. The decoded L3 message may then beused to confirm the blind detection result. When results differ,however, the process may be repeated. In another embodiment of thepresent invention, the mobile unit may use either blind detection or L3message decoding to determine a presence or absence of transmitdiversity among neighboring base stations as well as a selected basestation. In yet another embodiment of the present invention the mobileunit may receive transmit diversity information together with long codegroup information about neighboring base stations from the selected basestation via L3 message decoding.

[0047] It is understood that the inventive concept of the presentinvention may be embodied in a mobile communication system as well ascircuits within the mobile communication system. It is to be furtherunderstood that numerous changes in the details of the embodiments ofthe invention will be apparent to persons of ordinary skill in the arthaving reference to this description. It is contemplated that suchchanges and additional embodiments are within the spirit and true scopeof the invention as claimed below.

What is claimed:
 1. A circuit, comprising: a measurement circuit coupledto receive an input signal from at least one of a first antenna and asecond antenna of a transmitter, the measurement circuit producing anoutput signal corresponding to the input signal; and a comparatorcircuit coupled to receive the output signal and a first referencesignal, the comparator circuit arranged to produce a control signal inresponse to a comparison of the output signal and the first referencesignal.
 2. A circuit as in claim 1, wherein the comparator circuit isfurther coupled to receive a second reference signal and wherein thecomparator circuit arranged to produce the control signal in response toa comparison of the output signal, the first reference signal and thesecond reference signal.
 3. A circuit as in claim 1, wherein themeasurement circuit further comprises: an estimate circuit coupled toreceive the input signal, the estimate signal producing plural estimatesignals corresponding to the first antenna and the second antenna,respectively; an averaging circuit coupled to receive the estimatesignals, the estimate circuit arranged to produce respective averages ofthe plural estimate signals; and a ratio circuit coupled to receive therespective averages, the ratio circuit arranged to produce an outputsignal corresponding to a ratio of the respective averages.
 4. A circuitas in claim 1, wherein the input signal comprises at least one pilotsymbol of a wideband code division multiple access signal.
 5. A circuitas in claim 1, wherein the input signal comprises a plurality of pilotsymbols and wherein the output signal comprises a ratio of the pluralityof input signals.
 6. A circuit as in claim 1, further comprising: aDoppler estimate circuit coupled to receive the input signal, theDoppler estimate circuit arranged to apply an output signalcorresponding to a Doppler frequency of the input signal to themeasurement circuit; and a delay profile estimate circuit coupled toreceive the input signal, the delay profile estimate circuit arranged toapply an output signal to the measurement circuit corresponding toselected multipath signals.
 7. A circuit as in claim 1, furthercomprising a channel estimate circuit coupled to receive the outputsignal, the channel estimate circuit arranged to produce a variablenumber of channel estimates corresponding to the output signal.
 8. Acircuit as in claim 7, further comprising a phase correction circuitcoupled to receive a data signal and the variable number of channelestimates, the phase correction circuit arranged to correct the datasignal in response to the variable number of channel estimates.
 9. Amethod of processing signals for a communication system, comprising thesteps of: receiving an input signal from at least one of a plurality ofantennas; measuring the input signal; producing an output signalcorresponding to the measured input signal; comparing the output signalto a first reference signal; producing a first control signal inresponse to the step of comparing when the output signal has a valueless than a value of the first reference signal.
 10. A method as inclaim 9, further comprising the steps of: comparing the output signal toa second reference signal; and producing a second control signal inresponse to the step of comparing when the output signal has a valuegreater than a value of the second reference signal.
 11. A method as inclaim 10, further comprising the step of producing a third controlsignal in response to the step of comparing when the output signal has avalue between the value of the first reference signal and the value ofthe second reference signal.
 12. A method as in claim 10, furthercomprising the steps of: producing a plurality of channel estimates inresponse to one of the first control signal and the second controlsignal; and producing less than the plurality of channel estimates inresponse to the other of the first control signal and the second controlsignal.
 13. A method as in claim 9, further comprising the steps of:producing an output signal corresponding to a Doppler frequency of theinput signal; and producing an output signal corresponding to selectedmultipath signals.
 14. A circuit, comprising: an estimate circuitcoupled to receive an input signal from at least one of a plurality oftransmit antennas and coupled to receive a control signal, the controlsignal corresponding to a number of the at least one of a plurality oftransmit antennas, the estimate circuit selectively producing a firstestimate signal and a second estimate signal in response to the controlsignal; a correction circuit coupled to receive the input signal, thefirst estimate signal and the second estimate signal, the correctioncircuit producing a corrected input signal; a combiner circuit coupledto receive the corrected input signal, the combiner circuit producing acombined input signal; and a decoder circuit coupled to receive thecombined input signal, the decoder circuit arranged to decode thecombined input signal, thereby producing the control signal.
 15. Acircuit as in claim 14, further comprising: a measurement circuitcoupled to receive the input signal, the measurement circuit producingan output signal corresponding to the input signal; and a comparatorcircuit coupled to receive the output signal, a first reference signaland a second reference signal, the comparator circuit arranged toproduce a second control signal in response to a comparison of theoutput signal, the first reference signal and the second referencesignal.
 16. A circuit as in claim 14, wherein the input signal comprisesat least one pilot symbol of a wideband code division multiple accesssignal.
 17. A circuit as in claim 14, wherein the control signalcomprises a transmit diversity signal.
 18. A method of processingsignals for a communication system, comprising the steps of: receivingan input signal from at least one of a plurality of transmit antennas;receiving a control signal having a value corresponding to a number ofthe at least one of a plurality of transmit antennas; selectivelycombining the input signal from the at least one of a plurality oftransmit antennas in response to the control signal; decoding the inputsignal, thereby producing the control signal.
 19. A circuit as in claim18, wherein the control signal comprises a transmit diversity signal.20. A circuit as in claim 18, wherein the input signal comprises a datasignal of a primary common control physical channel.
 21. A communicationcircuit, comprising: an estimate circuit coupled to receive a controlsignal and coupled to receive a plurality of input signals from arespective plurality of remote transmitters, each remote transmitterhaving at least one transmit antenna, the control signal correspondingto a number of the at least one transmit antenna, the estimate circuitselectively producing a first estimate signal and a second estimatesignal in response to the control signal; a correction circuit coupledto receive the input signal, the first estimate signal and the secondestimate signal, the correction circuit producing a corrected inputsignal; a combiner circuit coupled to receive the corrected inputsignal, the combiner circuit producing a combined input signal; adecoder circuit coupled to receive the combined input signal, thedecoder circuit arranged to decode the combined input signal, therebyproducing the control signal; and a memory circuit arranged to storeeach said control signal corresponding to said respective plurality ofremote transmitters.
 22. A communication circuit as in claim 21, whereineach of the control signal is a transmit diversity signal.
 23. Acommunication circuit as in claim 21, wherein said selectively producingcomprises producing only the first estimate signal in response to afirst logic state of the control signal and producing the first and thesecond estimate signals in response to a second logic state of thecontrol signal.
 24. A circuit as in claim 21, wherein each of the firstand second estimate signals is a Rayleigh fading parameter estimate.